This invention relates to a process for the polymerization of bulky norbornene derivatives and to polymers obtained thereby. In one aspect, the invention relates to a process for the polymerization of specific bulky norbornene monomers to provide copolymers showing tailored product properties such as increased glass transition temperatures.
Extensive research efforts have been directed to the manufacture of polymers having high glass transition temperatures in combination with other desired properties. This appears, for example, from Japanese Patent Applications No. 61-293,208 and No. 63-092,625, U.S. Pat. No. 4,568,660, U.S. Pat. No. 3,718,474 and European Patent No. 0142861.
Japanese patent application No. 61-293,208 discloses the ring-opening polymerization of a copolymer in a reaction injection molding (RIM) process involving at least two norbornene-type monomers in the presence of a catalyst containing an inorganic tungsten compound and an activator to form a molded copolymer having an acceptable thermal resistance. Disclosed comonomers include tetracyclododecene, methyltetracyclododecene, dimethyltetracyclododecene, ethyltetracyclododecene and propyltetracyclododecene, and preferably at least one of 2-norbornene and dicyclopentadiene and at least one tetracyclododecene are used in a ratio of 5-8% by weight and 20-95% by weight, respectively, in a copolymerization catalyzed by a tungsten compound such as WCl.sub.6 or WOCl.sub.4 and an activator such as a dialkylaluminium monohalide, an aluminium sesquihalide, a trialkylaluminium and/or an aluminium trihalide as a metathesis catalyst system.
Japanese Patent Application No. 63-092,625 discloses moldings of crosslinked polymer obtained by polymerization in bulk, in the presence of a metathesis polymerization catalyst system, of a monomer mixture of 1:1 adducts obtained by Diels-Alder reaction between 3a,4,7,7a-tetrahydroindene and cyclopentadiene, or of these adducts and one or more other metathesispolymerizable monomers. However, it will be appreciated that the monomers as specified as MOHF and MBHI are bifunctional and provide a crosslinked polymer. More particularly in the examples as described only a TPA blend is used, comprising a 1:2:2 mixture of MOHG, MBHI and cyclopentadiene trimer (also being bifunctional), whereas no relatively high glass transition temperatures are mentioned. The highest glass transition temperature mentioned is 126.degree. C., and average values are about 110.degree. C. By post curing at 280.degree. C., this glass transition temperature seems to be increased to at most 165.degree. C., with an average value of about 140.degree. C.
U.S. Pat. No. 4,568,660 discloses, in column 32, lines 58-68 and in column 33, lines 1-32, respectively, the addition of a comonomer having two or more strained, reactive double bonds that will open during the polymerization, in order to increase the number of crosslinks, or a comonomer which contains four or more rings so that rotation or movement of the resulting backbone will be more constrained, in order to provide higher Tg in the polymer. As examples of useful norbornene type monomers are mentioned 1:1 Diels-Alder adducts of cyclopentadiene with norbornene, norbornadiene and 1,5-cyclooctadiene, the adducts of cyclopentadiene with polyfunctional acrylates, such as trimethylolpropane triacrylate and the like, and the 2:1 adduct of cyclopentadiene with diallyl adipate. Substantial increases in the crosslink density (as measured by the degree of swelling of the copolymers) are reported with copolymers made from dicyclopentadiene (DCPD) and the cyclopentadiene adducts with norbornadiene, trimethylpropane triacrylate, ethylene glycol diacrylate and ethylene glycol dimethacrylate.
U.S. Pat. No. 3,718,474 discloses, in column 4, lines 52-58, the preparation of a copolymer of DCPD and acenaphthylene to be used in an exposure assembly for imagewise exposing a layer of a solid soluble polymer which is crosslinked to insoluble condition upon exposure to light.
European Patent No. 142,861 discloses a reaction injection molding method for making a crosslinked thermoset polymer containing units derived from DCPD, in the presence of an organoaluminium or alkylaluminium halide activator. In this method not more than 20% of the DCPD units are replaced by other polymerizable units and the catalyst is a pentavalent tantalum catalyst represented by the formula Ta--Y.sub.5, wherein --Y is a) a halide, b) an alkoxy having the formula --O--R in which the organic radical R is a hydrocarbyl containing from 1 to 10 carbon atoms, c) an aryloxy having the formula --O--Ar, wherein the radical Ar is an aromatic radical containing from 1 to 3 aromatic rings, or d) an acyloxy having the formula OOCR.sup.1, in which the organic radical R.sup.1 is a hydrocarbyl containing from 1 to 10 carbon atoms. The other cycloolefin monomers are selected from norbornene, norbornadiene, cyclopentene, dimethanehexahydronaphthalene and dimethaneoctahydronaphthalene.
In spite of the efforts discussed above, there remains a growing need for an economical process for the manufacture of polymers showing tailored product properties such as an increased glass transition temperature which can be obtained without post-treatment of the polymer. It is therefore an object of the invention to provide such a process by using monomers having a specifically-adapted structure.